This invention relates generally to screen printing, such as used in electronic device fabrication, and more particularly the invention relates to an improved ink stop when printing to the edge of an object.
Screen printing has long been used in printing designs on objects, such as cloth, and is used in the electronics industry for printing electrical component designs such as contacts or interconnects with enchant resist or plating resist whereby the components can thereafter be formed by selective metal etching or metal plating. The fabrication of photovoltaic cells also uses screen printing.
Typically, a stencil is embedded in a screen made from silk, metal, or plastic, that controls the ink forced through the screen by the action of a roller or squeegee, thus producing a printed image. In semiconductor processing, such as in solar cell fabrication, it is sometimes necessary-to print the image up to the edge of tile wafer. If the ink is allowed to be printed outside the wafer, a buildup of ink can occur that contaminates the screen, support platen, and subsequent wafers. Further, the wafers can vary in size or in placement on the platen thereby moving the edge slightly. Thus, the problem can be exacerbated by wafers varying in size or in placement on the support platen.
Heretofore, the screen stencil has been made as close as possible to but inside the edge of the wafer. Thus the image is not printed to the very edge of the wafer. Variation in the position of the edge can make the non-printed margin larger, or reduce the margin to zero, thereby allowing the ink to accumulate and cause contamination.
The present invention is directed to providing an improved screen print ink stop when printing to the edge of a wafer or other object.
In accordance with the invention, gas pressure is provided at the edges of an object such as a wafer to oppose ink flow around the edges during screen printing, thereby allowing printing to the very edge of the wafer without incurring contamination from the ink.
In accordance with a preferred embodiment of the invention, a platen for supporting an object during screen printing is provided with gas vents near the edge of the supported object whereby gas pressure opposes ink flow around the edge and thereby prevents the flow of ink to the platen. The gas vents can be any suitable exhaust, such as a groove or a plurality of holes, for example. The gas can be air, an inert gas, or nitrogen, for example.
The invention and objects and features thereof will be more readily apparent from the following detailed description and appended claims, when taken with the drawings.